Methods and Apparatus for Performing Link Adaptation Processes in a Network

ABSTRACT

Embodiments described herein relate to methods and apparatus for performing link adaptation processes in a network. A method in a transmitting node in a wireless local area network comprises obtaining a first traffic flow for transmitting to a receiving node, wherein the first traffic flow is associated with a first category based on a reliability requirement associated with the first traffic flow; selecting a first link adaptation process from a plurality of link adaptation processes based on the first category; and transmitting the first traffic flow to the receiving node based on the first link adaptation process.

TECHNICAL FIELD

Embodiments described herein relate to method and apparatus fortransmitting traffic flows from a transmitting device to a receivingdevice in a wireless local area network.

BACKGROUND

Generally, all terms used herein are to be interpreted according totheir ordinary meaning in the relevant technical field, unless adifferent meaning is clearly given and/or is implied from the context inwhich it is used. All references to a/an/the element, apparatus,component, means, step, etc. are to be interpreted openly as referringto at least one instance of the element, apparatus, component, means,step, etc., unless explicitly stated otherwise. The steps of any methodsdisclosed herein do not have to be performed in the exact orderdisclosed, unless a step is explicitly described as following orpreceding another step and/or where it is implicit that a step mustfollow or precede another step. Any feature of any of the embodimentsdisclosed herein may be applied to any other embodiment, whereverappropriate. Likewise, any advantage of any of the embodiments may applyto any other embodiments, and vice versa. Other objectives, features andadvantages of the enclosed embodiments will be apparent from thefollowing description.

Traffic Sensitive Network (TSN) comprises an enhanced Ethernettechnology which may provide guaranteed data transport with bounded lowlatency, low delay variation, and extremely low loss. TSN includes a setof components such as Synchronization, Reliability, Latency and ResourceManagement.

TSN technology is expected to be an enabler for industrial automation.TSN includes technologies like packet pre-emption on the Ethernetmedium. For example, packet pre-emption works by stopping a frametransmission on the wire, replaces it with a priority transmission andthen resumes the original stopped frame transmission.

A type of traffic present in most industrial applications is periodictraffic, for example, in process automation where sensor reports, andactuation commands are created periodically. When serving periodictraffic, the TSN system reduces the delay variation (jitter) of servedpackets. As the information carried on the traffic is used in almost areal-time fashion high reliability may be required (very low packetloss).

Wireless Local Area Network (WLAN), for example Wi-Fi, is a wirelesscommunication system operating in Industrial Scientific and Medical(ISM) bands. There are several amendments of WLAN, for example, IEEE802.11a/b/n/ac/ax. It is usually deployed as a star system where theAccess Point (AP) is a device having a coordinator node (role) and thestations (STAs) are associated to APs. The AP maintains a Basic ServiceSet (BSS) to which the STAs are associated.

The WLAN system uses the Hybrid Coordination Function (HCF) whichdefines the EDCA (enhanced distributed channel access). The EDCA allowsSTAs to get access to the wireless medium (WM) via a listen-before talkprocedure. This procedure is also known as Clear Channel Assessment(CCA).

In the IEEE 802.11ax, data from mobile stations (STAs) can be polled bythe AP via trigger frames. In this case, the random access procedure iscarried out at the AP, and STAs reply to the trigger frames if they havebeen scheduled explicitly. IEEE 802.11ax also allows multi-user uplink(UL) access via OFDMA where multiple STAs may reply to the same triggerframe on orthogonal frequency resources. There may also be triggerframes for common access which allows STAs to compete for orthogonalfrequency resources via the OFDMA random access back-off (OBO). Triggerframes for explicit access and common access may be carried by the samephysical packet.

A Minstrel rate adaptation algorithm is based on an acknowledgmentfeedback algorithm. It is used by many Linux wireless drivers such asMad WIFI, Ath5k, and Ath9k. There are three main design concepts for theMinstrel adaptation algorithm: a retry chain mechanism, the ratedecision process and the statistic calculations.

The Minstrel algorithm uses a process called a multi-rate retry chainwhich reacts to short term fluctuations in channel quality. It consistsof four rate (r_(i)) count (c_(i)) pairs r0/c0, r1/c1, r2/c2 and r3/c3.The packet is first transmitted at rate r0 for c0 attempts. If theattempts fail, the packet is then transmitted using rate r1 for c1attempts. The process is continued until the packet is successfullytransmitted or discarded after c0+c1+c2+c3 un-successful transmissionattempts.

The values for r0, r1, r2 and r3 in the retry chain may be selected indifferent ways which depends on type of transmission used. The Minstreladaptation algorithm may use either normal transmission which occurs 90%of the time or sampling transmission which occurs for the remaining 10%of packets. Error! Reference source not found. gives a summary of therate selection decisions for this implementation of the algorithm. Innormal transmission, the r values in the retry chain are selected in away that r0 is the rate which achieves the highest expected throughput,r1 is the rate with the second highest expected throughput, r2 is therate with the highest probability of success, and finally r3 is set tothe lowest available data rate. In sampling transmission, the r valuesare selected in a way that r0 is set to the higher value either from thesample rate (which comprises a randomly selected rate to be testedduring the sampling transmission) or the rate with the highest expectedthroughput, and r1 is set to the lower value among two. r2 is the ratewith the highest probability of success and the r3 is the lowestavailable rate.

TABLE 1 Table 1 illustrates an example of a Minstrel Algorithm. SamplingTransmission Normal Rate Random < Best Random > Best Transmission r0Best rate Random rate Best rate r1 Random rate Best rate Second bestrate r2 Best probability Best probability Best probability r3 Base rateBase rate Base rate

The final step of the Minstrel algorithm may be to calculate theprobability of success and expected throughput for each data rate.Minstrel maintains the probability of successful transmission at eachdata rate as an Exponentially Weighted Moving Average (EWMA). Thisprobability is based on the historical success rate of packettransmissions at each data rate. This probability is used to estimatethe throughput of each rate and the retry chain is re-evaluated based onthis estimate every 100 ms. In each 100 ms sampling window, the successrate is calculated for each randomly selected data rate based on thehistorical observation of packet successes and failures. If a randomlyselected data rate provides either a higher rate than the previous ratesused during normal transmission, or a higher probability of success, therandom rate may then be used during normal transmission.

Link adaptation processes or algorithms for Wi-Fi, for example betweenan AP and a STA, do not currently consider that the transmitted packetsmay have different reliability requirements. As the link adaptationalgorithm or process, for example, the Minstrel adaptation algorithm,adapts to varying channel conditions, the algorithms may loose packetswhen trying sampling new data rates, i.e. during sampling transmission,to increase bitrates (test new bitrates) as they operate with a trialand error approach without channel state/quality feedback. The LinkAdaptation for WLAN may therefore currently be based purely onacknowledgment feedback after a successful reception.

SUMMARY

According to some embodiments there is provided a method in atransmitting node in a wireless local area network. The method comprisesobtaining a first traffic flow for transmitting to a receiving node,wherein the first traffic flow is associated with a first category basedon a reliability requirement associated with the first traffic flow;selecting a first link adaptation process from a plurality of linkadaptation processes based on the first category; and transmitting thefirst traffic flow to the receiving node based on the first linkadaptation process.

According to some embodiments there is provided a transmitting node in awireless local area network. The transmitting node comprises processingcircuity configured to obtain a first traffic flow for transmitting to areceiving node, wherein the first traffic flow is associated with afirst category based on a reliability requirement associated with thefirst traffic flow; select a first link adaptation process from aplurality of link adaptation processes based on the first category; andtransmit the first traffic flow to the receiving node based on the firstlink adaptation process.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a method in a transmitting node in a wireless localarea network according to some embodiments;

FIG. 2 illustrates an example of a method for performing the second linkadaptation process for the second traffic flow according to someembodiments;

FIG. 3 illustrates an example of a method for performing the first linkadaptation process according to some embodiments;

FIG. 4 illustrates a transmitting node comprising processing circuitryaccording to some embodiments.

DESCRIPTION

The following sets forth specific details, such as particularembodiments for purposes of explanation and not limitation. But it willbe appreciated by one skilled in the art that other embodiments may beemployed apart from these specific details. In some instances, detaileddescriptions of well-known methods, nodes, interfaces, circuits, anddevices are omitted so as not obscure the description with unnecessarydetail. Those skilled in the art will appreciate that the functionsdescribed may be implemented in one or more nodes using hardwarecircuitry (e.g., analog and/or discrete logic gates interconnected toperform a specialized function, ASICs, PLAs, etc.) and/or using softwareprograms and data in conjunction with one or more digitalmicroprocessors or general purpose computers that are specially adaptedto carry out the processing disclosed herein, based on the execution ofsuch programs. Nodes that communicate using the air interface also havesuitable radio communications circuitry. Moreover, the technology mayadditionally be considered to be embodied entirely within any form ofcomputer-readable memory, such as solid-state memory, magnetic disk, oroptical disk containing an appropriate set of computer instructions thatwould cause a processor to carry out the techniques described herein.

Hardware implementation may include or encompass, without limitation,digital signal processor (DSP) hardware, a reduced instruction setprocessor, hardware (e.g., digital or analog) circuitry including butnot limited to application specific integrated circuit(s) (ASIC) and/orfield programmable gate array(s) (FPGA(s)), and (where appropriate)state machines capable of performing such functions.

In terms of computer implementation, a computer is generally understoodto comprise one or more processors, one or more processing modules orone or more controllers, and the terms computer, processor, processingmodule and controller may be employed interchangeably. When provided bya computer, processor, or controller, the functions may be provided by asingle dedicated computer or processor or controller, by a single sharedcomputer or processor or controller, or by a plurality of individualcomputers or processors or controllers, some of which may be shared ordistributed. Moreover, the term “processor” or “controller” also refersto other hardware capable of performing such functions and/or executingsoftware, such as the example hardware recited above.

Embodiments described herein take into account the category of differenttraffic flows, where the category is based on a reliability requirementassociated with each traffic flow, when determining a link adaptationprocess for a particular traffic flow.

For example, a TSN traffic flow may require higher reliability than avoice traffic flow and thus the link adaptation process may be selectedbased on this requirement. In addition, in case there are severalconcurrent flows in a communication link, embodiments described hereinmay perform a link adaptation process per traffic flow, and may test newmodulation and coding schemes (MCSs) (or data rates) using a trafficflow with the lowest reliability requirements on the communication linkin order to use well-tested MCSs (or data rates) (best probable) for thetraffic flows having higher reliability requirements.

By utilizing knowledge of the reliability requirement associated witheach traffic flow, the link adaptation process can be selected suchthat, for traffic flows requiring a higher level of reliability, theprobability of losing packets due to sampling transmissions is reduced.

Furthermore, by utilizing knowledge gained in the link adaptationprocess for the lower reliability traffic flow to influence the linkadaptation process for the higher reliability traffic flow, the datarates used in the higher reliability traffic flow may still benefit fromthe trial and error processing performed by the link adaption processfor the lower reliability traffic flow.

FIG. 1 illustrates a method in a transmitting node in a wireless localarea network. It will be appreciated that the transmitting node maycomprise a mobile station (STA) or an access point (AP) in acommunications link.

In step 101, the method comprises obtaining a first traffic flow fortransmitting to a receiving node, wherein the first traffic flow isassociated with a first category based on a reliability requirementassociated with the first traffic flow. It will be appreciated that thereceiving node may comprise a STA or an AP in a communications link.

For example, traffic flows for transmission to the receiving node may becategorized according to their reliability requirement. For example,reliability categories may be defined such as “low” and “high or use ahigher granularity of possible categories may be used and the differenttraffic flows may be associated to each of these categories.

In some examples, a TSN traffic flow will have a reliability requirementbased on the application generating and consuming the data. Therefore insome examples, any type of TSN traffic may have a higher reliabilityrequirement than a voice flow, or video flow, or best effort flow, orbackground flow.

It will be appreciated that this categorization of the traffic flows maybe performed by the transmitting device, or may be performed by anothernode in the network. In some example therefore, the first traffic flowmay be received at the transmitting device along with some indication ofthe category associated with the first traffic flow.

In step 102, the method comprises selecting a first link adaptationprocess from a plurality of link adaptation processes based on the firstcategory.

For example, there may be at least two link adaption processes. A firstlink adaptation process may be for traffic flows associated with acategory for higher reliability requirements, whereas, a second linkadaptation process may be for traffic flows associated with a categoryfor lower reliability requirements. It will be appreciated that anynumber of link adaptation processes may be available, and that each linkadaptation process may be associated with one or more categories.

In step 103, the method comprises transmitting the first traffic flow tothe receiving node based on the first link adaptation process.

In some examples, therefore, the method may further comprise obtaining asecond traffic flow for transmitting to the receiving node, wherein thesecond traffic flow is categorised into a second category based on areliability requirement associated with the second traffic flow;selecting a second link adaptation process from the plurality of linkadaptation processes based on the second category; and transmitting thesecond traffic flow to the receiving node based on the second linkadaptation process.

For example, the first traffic flow may comprise a traffic flow having ahigh reliability requirement, for example a TSN traffic flow. The firstcategory may therefore comprise a category associated with highreliability. The first link adaptation process may therefore compriseselecting a data rate for transmitting the first traffic flow byprioritising a probability of success for the data rate. In other words,as the traffic flows associated with the first category have highreliability requirements, the first link adaptation process mayprioritise the probability of success for the transmission of packetsrather than, for example, attempting to increase the expectedthroughput.

The second traffic flow may comprise a traffic flow having a lowreliability requirement, for example a voice traffic flow. The secondcategory may therefore comprise a category associated with lowreliability. The second link adaptation process may therefore compriseselecting a data rate for transmitting the second traffic flow byprioritizing the expected throughput for the data rate. In other words,as reliability is less important for the traffic flows in the secondcategory, the link adaptation process can prioritise finding data ratesgiving a high expected throughput.

FIG. 2 illustrates an example of a method for performing the second linkadaptation process for the second traffic flow. This method represents amethod performed for traffic flows associated with a low reliabilitycategory.

In step 201 the second link adaptation process selects a data rate fortransmission of a packet in the second traffic flow. For example,selecting a modulation and coding scheme effectively selects a data ratefor transmission of the second traffic flow. The packet is transmitted.

The second link adaptation process may for example, operate, asdescribed by the Minstrel algorithm above, by selecting the rateaccording to acknowledgment feedback from transmission of previouspackets. It will be appreciated that any link adaptation process may beused here. For example, any link adaptation process that tests datarates during sampling transmission in order to collect statisticsrelating to the tested data rates.

In step 202, statistics relating to the best rate, best probability andthe base rate are gathered based on acknowledgments for the transmittedpacket in step 201. For example, step 202 may comprise updatinginformation relating to one or more of a probability of success and anexpected throughput associated with at least one sample data rate. Theat least one sample data rate may comprise the data rates used by thesecond link adaptation process during transmission of the second trafficflow.

In step 203 the method comprises determining whether there are furtherpackets to transmit on the second traffic flow. If further packets areto be transmitted, the method returns to step 201. If no further packetsare to be transmitted, the method ends.

For the first link adaptation process different principles may beapplied. For example the first link adaptation process may consider thereliability restriction and select the MCS/data rates to minimize packererror rate instead of maximizing bitrate.

The first link adaptation process will obtain information, statistics,gathered by the second link adaption process on the same radio link.Thus, it may uses the MCS/data rates with best probability of success asdetermined by the second link adaptation process to meet its packererror rate target.

When packet error rate is lower than the packet error rate target(packet success rate is higher than the packet success target), the linkadaptation for higher reliability categories may test new MCS/data ratesas dictated by the first link adaptation process.

FIG. 3 illustrates an example of a method for performing the first linkadaptation process according to some embodiments.

In step 301, the method comprises obtaining the updated informationprovided by the second link adaptation process in 202.

In step 302, the method comprises selecting a first data rate for thetransmission of a packet from the at least one sample data rate based onthe updated information from the second link adaptation process. Thisselection may also be made based on any updated information provided bythe first link adaptation process in the transmission of previouspackets. As previously, the selection of a data rate may be made by theselection of a MCS. It will be appreciated that, as the first linkadaptation process may prioritise the probability of success associatedwith a data rate, the selection of the first data rate may be made tomaximise the probability of success.

In step 303, the method comprises determining whether the probability ofsuccess associated with the first data rate meets a first condition. Forexample, the first condition may comprise a condition that theprobability of success associated with the first data rate is above afirst threshold.

If the first condition is not met, the method may pass to step 304 inwhich the method comprises selecting a third data rate associated with ahigher probability of success than the first data rate. The method thenpasses to step 305 in which a packet of the traffic flow is transmittedusing the third data rate. Step 305 may also comprise updatinginformation relating to the probability of success and the expectedthroughput associated with the third data rate.

Returning to step 303, if the first condition is met, the method may insome embodiments pass to step 305 in which a packet of the traffic flowis transmitted using the first data rate. Step 305 may also compriseupdating information relating to the probability of success and theexpected throughput associated with the first data rate. In thisembodiment there may be no second condition as described below withrespect to step 306.

However, in some alternative embodiments, if the first condition is met,the method passes to step 306 in which the method comprises determiningwhether the probability of success associated with the first data ratemeets a second condition. For example, the second condition may comprisea condition that the probability of success associated with the firstdata rate is below a second threshold wherein the second threshold ishigher than the first threshold.

Responsive to the second condition being met, the method passes to step305 in which the method comprises transmitting the packet of the firsttraffic flow using the first data rate. Step 305 may also compriseupdating information relating to the probability of success and theexpected throughput associated with the first data rate.

Responsive to the second condition not being met the method passes tostep 307 in which the method comprises selecting a second data rateassociated with a higher expected throughput than the first data rate.The method then passes to step 305 in which a packet of the traffic flowis transmitted using the second data rate. Step 305 may also compriseupdating information relating to the probability of success and theexpected throughput associated with the second data rate.

Following step 305, the method may pass to step 308 in which the methodcomprises determining whether there are further packets to transmit onthe first traffic flow. If further packets are to be transmitted, themethod returns to step 301. If no further packets are to be transmitted,the method may end.

In other words, the process of FIG. 3 described above allows the firstlink adaptation process to make use of information collected by thesecond link adaptation process, and of any information collected by thefirst link adaptation process in the transmission of previous packets,to select a first data rate. If this selection of the first data ratemeets the first condition, or the first condition and the secondcondition, the first link adaptation process may transmit the packetwithout performing any sampling of new rates. However, should either orboth of the first condition or second condition not be met, the firstlink adaptation process may sample new rates as dictated by, forexample, the Minstrel link adaptation algorithm as described above.

The methods described in FIGS. 2 and 3 may for example, mean that thebit rates selected in the second link adaptation process may beoptimized for highest throughput as the original Minstrel algorithmdictates, and the bit rates selected in the first link adaptationprocess may be optimized for minimizing packet error rate.

The methods described above may be applied to any link adaptationalgorithm based on acknowledgment feedback such as the Minstrelalgorithm for Wi-Fi, or other algorithms used in Wi-Fi systems. Incontrast to link adaptation algorithms based on channel status/qualityinformation which can track the channel changes more precisely, theproposed methods may for example, set a packet error rate target basedon the reliability requirement for each link adaption process linked toa reliability requirement.

In some examples, the transmitting node may not receive a traffic flowfor transmission in the second category. In these examples, thetransmitting node may generate the second traffic flow by generating adummy traffic flow comprising dummy packets.

This dummy traffic flow may comprise packets including a physical layerpayload for which a data rate or modulation coding scheme can be set bya link adaptation process (for example as described above). We can callthese packets, no-information MAC packets, or dummy packets, in contrastto Wi-Fi non-data packets (NDP) which don't have a physical layerpayload and hence are not subject to link adaptation process rules. Byhaving a TSN traffic flow and a no-information traffic flow, the methoddescribed with reference to FIG. 2 may be applied to the no-informationtraffic flow, and the method described with reference to FIG. 3 may beapplied to the TSN traffic flow.

FIG. 4 illustrates a transmitting node 400 comprising processingcircuitry (or logic) 401. The processing circuitry 401 controls theoperation of the transmitting node 400 and can implement the methoddescribed herein in relation to a transmitting node 400. The processingcircuitry 401 can comprise one or more processors, processing units,multi-core processors or modules that are configured or programmed tocontrol the transmitting node 400 in the manner described herein. Inparticular implementations, the processing circuitry 401 may comprise aplurality of software and/or hardware modules that are each configuredto perform, or are for performing, individual or multiple steps of themethod described herein in relation to the transmitting node 400.

Briefly, the processing circuitry 401 of the transmitting node 400 isconfigured to obtain a first traffic flow for transmitting to areceiving node, wherein the first traffic flow is associated with afirst category based on a reliability requirement associated with thefirst traffic flow; select a first link adaptation process from aplurality of link adaptation processes based on the first category; andtransmit the first traffic flow to the receiving node based on the firstlink adaptation process.

In some embodiments, the transmitting node 400 may optionally comprise acommunications interface 402. The communications interface 402 of thetransmitting node 400 can be for use in communicating with other nodes,such as other virtual nodes. For example, the communications interface402 of the transmitting node 400 may be configured to transmit to and/orreceive from other nodes requests, resources, information, data,signals, or similar. The processing circuitry 401 of the transmittingnode 400 may be configured to control the communications interface 402of the transmitting node 400 to transmit to and/or receive from othernodes requests, resources, information, data, signals, or similar.

Optionally, the transmitting node 400 may comprise a memory 403. In someembodiments, the memory 403 of the transmitting node 400 can beconfigured to store program code that can be executed by the processingcircuitry 401 of the transmitting node 400 to perform the methoddescribed herein in relation to the transmitting node 400.Alternatively, or in addition, the memory 403 of the transmitting node400, can be configured to store any requests, resources, information,data, signals, or similar that are described herein. The processingcircuitry 401 of the transmitting node 400 may be configured to controlthe memory 403 of the transmitting node 400 to store any requests,resources, information, data, signals, or similar that are describedherein.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. The word “comprising” does not excludethe presence of elements or steps other than those listed in a claim,“a” or “an” does not exclude a plurality, and a single processor orother unit may fulfil the functions of several units recited in theclaims. Any reference signs in the claims shall not be construed so asto limit their scope.

1-30. (canceled)
 31. A method in a transmitting node in a wireless localarea network, the method comprising: obtaining first and second trafficflows for transmitting to a receiving node; wherein the first trafficflow is categorized into a first category based on a reliabilityrequirement associated with the first traffic flow; wherein the secondtraffic flow is categorized into a second category based on areliability requirement associated with the second traffic flow; whereinthe first and second categories are different; selecting a first linkadaptation process from a plurality of link adaptation processes for thefirst category, and a second link adaptation process from the pluralityof link adaptation processes for the second category; wherein the firstand second link adaptation processes are different and the secondcategory is associated with lower reliability requirement than the firstcategory; and transmitting the first traffic flow to the receiving nodebased on the first link adaptation process; transmitting the secondtraffic flow to the receiving node based on the second link adaptationprocess; wherein the second link adaptation process comprises updatinginformation relating to a probability of success and/or an expectedthroughput associated with at least one sample data rate; and whereinthe first link adaptation process comprises selecting a first data ratefrom the at least one sample data rate based on the updated informationfrom the second link adaptation process.
 32. The method of claim 31,wherein the second link adaptation process comprises selecting a datarate for transmitting the second traffic flow by prioritizing theexpected throughput for the data rate.
 33. The method of claim 31,wherein the first link adaptation process comprises selecting a datarate for transmitting the first traffic flow by prioritizing aprobability of success for the data rate.
 34. The method of claim 31:further comprising transmitting, responsive to a probability of successassociated with the first data rate meeting a first condition, a packetof the first traffic flow using the first data rate; wherein the firstcondition comprises a condition that the probability of successassociated with the first data rate is above a first threshold.
 35. Themethod of claim 34: further comprising performing the transmitting thepacket of the first traffic flow using the first data rate responsive tothe probability of success associated with the first data rate meeting asecond condition; wherein the second condition comprises a conditionthat the probability of success associated with the first data rate isbelow a second threshold; wherein the second threshold is higher thanthe first threshold.
 36. The method of claim 35, further comprising:selecting, responsive to the probability of success associated with thefirst data rate not meeting the second condition, a second data rateassociated with a higher expected throughput than the first data rate;and transmitting the packet of the first traffic flow with the seconddata rate.
 37. The method of claim 34, further comprising: selecting,responsive to the probability of success associated with the first datarate not meeting the first condition, a third data rate associated witha higher probability of success than the first data rate; andtransmitting the packet of the first traffic flow with the third datarate.
 38. The method as of claim 31, wherein the obtaining comprisesgenerating the second traffic flow, responsive to the transmitting nodenot receiving a traffic flow for transmission in the second category, bygenerating a dummy traffic flow comprising dummy packets.
 39. The methodof claim 31, wherein the first link adaptation process comprises:updating information relating to a probability of success and/or anexpected throughput associated with at least one sample data rate; andselecting a first data rate from the at least one sample data rate basedon the updated information from the first link adaptation process.
 40. Atransmitting node in a wireless local area network, the transmittingnode comprising: processing circuitry; memory containing instructionsexecutable by the processing circuitry whereby the transmitting node isoperative to: obtain first and second traffic flows for transmitting toa receiving node; wherein the first traffic flow is associated with afirst category based on a reliability requirement associated with thefirst traffic flow; wherein the second traffic flow is categorized intoa second category based on a reliability requirement associated with thesecond traffic flow; wherein the first and second categories aredifferent; select a first link adaptation process from a plurality oflink adaptation processes for the first category, and a second linkadaptation process from the plurality of link adaptation processes forthe second category; wherein the first and second link adaptationprocesses are different and the second category is associated with lowerreliability requirement than the first category; and transmit the firsttraffic flow to the receiving node based on the first link adaptationprocess; transmit the second traffic flow to the receiving node based onthe second link adaptation process; wherein the second link adaptationprocess comprises updating information relating to a probability ofsuccess and/or an expected throughput associated with at least onesample data rate; and wherein the first link adaptation processcomprises selecting a first data rate from the at least one sample datarate based on the updated information from the second link adaptationprocess.
 41. The transmitting node of claim 40, wherein the instructionsare such that the transmitting node is operative to perform the secondlink adaptation process by selecting a data rate for transmitting thesecond traffic flow by prioritizing the expected throughput for the datarate.
 42. The transmitting of claim 41, wherein the instructions aresuch that the transmitting node is operative to perform the first linkadaptation process by selecting a data rate for transmitting the firsttraffic flow by prioritizing a probability of success for the data rate.43. The transmitting node of claim 40: wherein the instructions are suchthat the transmitting node is operative to transmit, responsive to aprobability of success associated with the first data rate meeting afirst condition, a packet of the first traffic flow using the first datarate; wherein the first condition comprises a condition that theprobability of success associated with the first data rate is above afirst threshold.
 44. The transmitting node of claim 43: wherein theinstructions are such that the transmitting node is operative to performthe transmitting the packet of first traffic flow using the first datarate responsive to the probability of success associated with the firstdata rate meeting a second condition; wherein the second conditioncomprises a condition that the probability of success associated withthe first data rate is below a second threshold; wherein the secondthreshold is higher than the first threshold.
 45. The transmitting nodeof claim 44, wherein the instructions are such that the transmittingnode is operative to: select, responsive to the probability of successassociated with the first data rate not meeting the second condition, asecond data rate associated with a higher expected throughput than thefirst data rate; and transmit the packet of the first traffic flow withthe second data rate.
 46. The transmitting node of claim 43, wherein theinstructions are such that the transmitting node is operative to:select, responsive to the probability of success associated with thefirst data rate not meeting the first condition, a third data rateassociated with a higher probability of success than the first datarate; and transmit the packet of the first traffic flow with the thirddata rate.
 47. The transmitting node of claim 40, wherein theinstructions are such that the transmitting node is operative to performthe obtaining by generating the second traffic flow, responsive to thetransmitting node not receiving a traffic flow for transmission in thesecond category, by generating a dummy traffic flow comprising dummypackets.
 48. The transmitting node of claim 40, wherein the instructionsare such that the transmitting node is operative to perform the firstlink adaptation process by: updating information relating to aprobability of success and/or an expected throughput associated with atleast one sample data rate, selecting a first data rate from the atleast one sample data rate based on the updated information from thefirst link adaptation process.